1. Field of the Invention
The present invention generally relates to an image forming apparatus such as a copier, a printer, a facsimile machine, a multifunction machine including at least two of those functions, etc., and sheet transport controlling method used therein, and more particularly, to an image forming apparatus including a sheet handling unit and sheet transport controlling method used therein.
2. Discussion of the Background Art
In general, an electrophotographic image forming apparatus, such as a copier, a printer, a facsimile machine, a multifunction machine including at least two of those functions, etc., includes an image reading unit that reads image information of an original document and an image forming unit that forms an image on a sheet of recording media according to the image information. The image forming unit forms an electrostatic latent image on an image carrier, develops the latent image with developer, and transfers the developed image (toner image) onto the sheet.
Some image forming apparatuses are provided with a sheet handling unit for performing post-processing, for example, aligning, sorting, stapling, and/or punching the sheets. Although the sheets can be discharged from a side of the image forming apparatus and the sheet handling unit can be attached to the side thereof, such a configuration makes the image forming apparatus bulkier.
At present, in many image forming apparatuses, a sheet discharge space is provided within an installation area of a main body thereof (hereinafter “housing-internal discharge type image forming apparatus”), for example, beneath the image reading unit, to make the image forming apparatus more compact as well as increase image formation speed.
In order to further reduce overall size of the image forming apparatus including the sheet handling unit, several approaches are known.
A known housing-internal discharge type image forming apparatus includes a compact sheet handling unit attached to a side thereof, and a relay transport member that transports a sheet between a sheet discharge space and the sheet handling unit. In this image forming apparatus, when the sheet is discharged without post-processing, the sheet is discharged to the sheet discharge space from a sheet discharge port that is different from a sheet discharge port connecting to the sheet handling unit.
In another known housing-internal discharge type image forming apparatus, a sheet handling unit is provided in a sheet discharge space in order to reduce the overall size of the image forming unit. In this image forming apparatus, the sheet handling unit can be within an installation area of a main body thereof, keeping the overall size compact.
Yet in another known housing-internal discharge type image forming apparatus, a sheet reverse path is formed using a sheet discharge space, and, in duplex printing mode, a sheet is reversed through the sheet reverse path after an image is formed on a first side thereof. In this configuration, because a sheet reverse unit to be attached to a side of the image forming apparatus is not necessary, the overall size thereof can be reduced. Further, the sheet reverse path can be provided separately from a sheet receiving part of the sheet handling unit located inside the housing of the image forming apparatus.
However, in such an image forming apparatus including the sheet handling unit mountable in the sheet discharge space located within the housing, the height of the image forming apparatus will be increased so as to attain a sufficiently large opening of the sheet discharge space to enable a user to check the sheet discharged thereinto and remove the sheet therefrom. Thus, it is difficult to balance the user's need for easy access to the sheet with the general need for compactness of the image forming apparatus.
More specifically, in the image forming apparatus including the sheet handling unit mountable in the sheet discharge space located within the housing, generally, an identical path is used to reverse the sheet after an image is formed on the first side and to discharge the sheet after an image is formed on a second side thereof, which is described in further detail with reference to FIG. 13.
FIG. 13 illustrates an example of the image forming apparatus including the sheet handling unit mountable in the sheet discharge space located within the housing.
As shown in FIG. 13, when a sheet handling unit 200Z is not mounted in a sheet discharge space 400, it is necessary to attach a discharge tray 41Z on which the sheets are stacked to the image forming apparatus. The sheet discharge tray 41Z should be located at a position lower than that of a sheet discharge port 30, and a vertical distance therebetween should be set so as to be able to stack the sheets neatly on the discharge tray 41Z when multiple sheets are discharged.
However, the location of the sheet discharge port 30 should be determined in consideration of location of a sheet receiving port 30A of the sheet handling unit 200Z that engages the sheet discharge port 30 as well. Because the location of the sheet receiving port 30A depends on the specific configuration of components of the sheet handling unit 200Z, such as a puncher, a stapler, etc., it will be higher than a preferred location of the sheet discharge port 30 with respect to the sheet discharge tray 41Z.
Therefore, the sheet discharge tray 41Z should be increased in height in accordance with the location of the sheet discharge port 30 with respect to the sheet receiving port 30A of the sheet handling unit 200Z, which reduce the sheet discharge space 400 in the vertical direction. Accordingly, visibility of the sheet discharged on the sheet discharge tray 41Z as well as accessibility thereto are degraded.
Further, in the case where the sheet reverse path (switchback reverse path) is provided separately from the sheet receiving part 30A of the sheet handling unit 200Z, because a second sheet discharge port is provided at a portion higher than that of the sheet receiving port 30A of the sheet handling unit 200Z, the sheet discharge space is relatively large in the vertical direction. Accordingly, the height of the image forming apparatus is increased, which degrades accessibility to the image reading unit provided on an upper portion thereof and increases the cost of the image forming apparatus.